I need to make another grey one so I can have two others flanking me at all times!

The seat has yet to be attached and I still have to trim the seams and add the attachment points etc. but the whole shebang as seen here is just over 30 ounces - still under the two pound mark - tape, excess fabric, and all.

So you recall the Lord Vader tube - pretty black fabric, very lightweight, and I had changed the seam profiles of the back of the seat and the inner diameter of the "U" section to be faceted to ostensibly facilitate the connection between the two parts.

Well, you win some, you lose some. I had a feeling that the apexes between the straight line segments on the "U" would be stressed, but I didn't go with my gut so basically at high pressure, the urethane coating delaminated under the localized stress and the fabric became porous. Instead of sealing up the fabric with glue on the outside, I wanted to "keep it clean" so I simply, and again against my better judgemet, moved the seam inward to get some "new coating" at the apexes. At any rate, this sealed the bladder, but the stresses were still there and when I put some lung into it, I got the dreaded POPssssssssss...

I guess I lost this one.

Anyway, I wasn't really completely satisfied with the geometry of the "U" and I was making compromises because of this so I took this opportunity to tweak the pattern and go for Prototype #3.

Voila! (I'm sad that I don't have any more of the Vader black fabric, but this blue is still pretty sexy...):

I feel MUCH better with the new geometry and I believe that it'll work out well. I also went back to the simple radii and think I have a good connection design.

Here's the package as-is with a ton of fabric left to trim off:

I'm bummed that it's crept up over the magic two pound number, but this fabric is a bit heavier than the black, and I think there should be a couple of ounces of scrap that I can shed to bring it back down.

BTW, here's what the thing packs down to, and with some compression, it can go smaller, though I think it's sufficiently small as is, no?

At any rate, I'll keep plugging with this new prototype. Things are very promising, but of course my engineer mind won't let me leave things be and I'm working on a new list of things to tweak...

I finally permanently attached the seat to the "U" section. One of the biggest difficulties of doing this is that the length of the arc around the inside of the "U" is much shorter than the length of the arc around the back of the seat (when deflated). When inflated the two arcs should be the same as the back of the seat puckers up and pulls in.

What I originally envisioned with the Vader Prototype was to have 5 segments to break up the arcs into the same percentage of the total curve and then weld them on center. The problem that I discovered in reality was that with only 5 segments I couldn't geometrically "pucker" the back of the seat without overlapping with the adjacent segment. Sheesh, this is hard to explain...

At any rate, with the newest Gen 3 (Hmm... Navy blue, Higashi Navy, Higashi Maru?) I broke up the two arcs into 15 (!!) segments which allowed a nice even pucker.

Check it!

Here is the assembly with the seat fully deflated. You can see even if the seat gets harpooned by a Lake Davis pike, you can still sit low and wet in the sling and kick home.

And here is the thing fully inflated with a temporary spread limiter installed. You're looking at the bottom of the tube here... The real deal will of course be cleaner!

Flip side (the side you sit on!):

Prototype fleet! (OG Proto1 is rolled up awaiting orders...) You can see from this photo that I've repaired Vader. Sure you saw his Tie Fighter go spinning out of control into deep space, but you couldn't REALLY have thought that you wouldn't see him again in the sequel? The repair allowed me to experiment with seam geometries, and though these tweaks most likely won't end up in the production model, data is data.

Next step on Higashi-maru will be to finish trimming the seams, install the spread limiter strap, the valve plug leashes, and glue on the attachment points.

Until I actually "take the plunge" I won't know if there are any further design details that I'll want to make on the next one, but so far from the looks of it I think I'm pretty damn near done with the design of the air holding system.